As can be gathered from the documents identified above, it is common practice in the control of fluid media to provide a ball valve or ball cock which can have a housing, an inlet passage and an outlet passage formed in the housing, a valve ball which can be provided with a passage, and a mechanism for rotating the ball to shift it between flow-permitting and flow-blocking positions. The ball can be received between seating rings which seal against the ball and in the flow-permitting position the aforementioned passages can be axially aligned. Usually the coaxial passages are of circular cross section.
Reference to a flowable medium here is intended to include not only a liquid which can entrain abrasive substances in a slurry or suspension, but also gaseous media such as gases and vapors which can entrain particulates.
In the fabrication and assembly of such ball valves, it is possible for offsets to occur between the passages as a result of fabrication and assembly tolerances. These offsets can result in the formation of free edges against which the flowable medium and any abrasives contained therein can impinge.
As a result, from a rheological point of view there can be pressure losses in addition to any flow-dependent wear which may detrimentally effect the life of the valves, its scaling effectiveness or the like. When these edges are involved in the sealing action, moreover, it cannot be excluded that the sealing function can fail.
These drawbacks are especially significant in applications in which the valve must constitute a so-called gate for the flow of solids, namely, in the control of gases which entrain solids like fly ash in connection with gas cleaning plants and the like.